Gelled acidic compositions

ABSTRACT

Aqueous acidic compositions gelled with a polymer having pendent amide or nitrile functions cross-linked by a monomer containing a plurality of -(CH2OR) groups bonded to amido nitrogen and a process for their preparation. The gelling system of this invention finds particular utility in explosive compositions based on an oxidizing agent and one or more fuels or sensitizers.

United States Patent Peterson Jan. 18, 1972 [54] GELLED ACIDICCOMPOSITIONS [72] Inventor: Marvin L. Peterson, Woodstown, NJ. [56]References Cited [73] Assignee: E. I. du Pont de Nemours and Company,UNITED STATES PATENTS Wilmington, 1391- 2,658,045 11 1953 Schildknecht..260/29.6 3 046 201 7/1962 White et a1 ....252/316 X 22 F1 d. A .201969 1 3,483,172 12/1969 Shibukawa et a1 ..260/29.6 x [21] Appl. No.:871,342

Primary ExaminerRichard D. Lovering Related U.S. Application Data Anomeyjohn F. Schmutz [62] Division of Ser. No. 663,495, Aug. 28, 1967, Pat.No.

3,507,720. [57] ABSTRACT Aqueous acidic compositions gelled with apolymer having [52] U.S. Cl ..252/3l5, 71/58, 71/59, pendent amide ornitrile functions cmSsJinked by a monomer 71/64 71/64 c, 252/855 252/792252/794, containing a plurality of -(CH OR) groups bonded to amido252/145, 252/186, 252/316 260/29-6 AN, 260/29-6 nitrogen and a processfor their preparation. The gelling CM system of this invention findsparticular utility in explosive [51] 1 13/00 compositions based on anoxidizing agent and one or more [58] 149/19, 20, 55, 56, 57, 60, fuelsor sensitizers 149/61, 67, 69, 74, 105; 252/315, 316,145; 260/296 AN,29.6 CM

18 Claims, No Drawings GELLED ACIDIC COMPOSITIONS CROSS-REFERENCE TOPRIOR APPLICATION This is a division of application Ser. No. 663,495,filed Aug. 28, 1967, now US. Pat. No. 3,507,720.

BACKGROUND OF THE INVENTION The handling of liquid acidic compositionshas long been a complicating factor in their use in various industriessuch as oil production, propellants, metallurgy, fertilizers andexplosives, due to the inherent corrosiveness and, in some cases, strongoxidizing capacity of the acids. In more recent years, there has beenincreased interest in developing means of safely handling acidiccompositions. This interest has been particularly evident in theexplosives industry particularly with respect to compositions containingan inorganic oxidizing agent together with sensitizer or fuel componentssince the discovery of the greater work potential of water-bearingcompositions containing these constituents. Since the constituents ofsuch explosive compositions exhibit varying degrees of solubility,difficulty was encountered in maintaining the homogeneity of aqueousexplosive compositions of this type. The use of such compositions forblasting in wet boreholes was still further complicated by the seepageof water into the explosive compositions, altering the constitution ofthe composition by dilution and leaching of the soluble components.

To help solve these problems, various thickeners or gelling agents havebeen used with slurried explosive compositions based on inorganicoxidizing salts. Satisfactory thickener systems for these compositionsare based on natural hydroxylated polymers such as naturalpolysaccharides, particularly galactomannan gums and their derivatives.

The versatility of these systems is increased by the provision ofvarious cross-linking agents which gel the compositions therebyincreasing the stability of the system and usually imparting otherbeneficial effects. Some variations in product consistency is possibleby varying the proportions of hydroxylated polymers and cross-linkingmonomers in the compositions, but usually water resistance is seriouslydeficient at concentrations low enough to provide readily pourablecompositions. In particular there is a now well-recognized need for agelling system for aqueous compositions which will provide stable,pourable compositions which exhibit good water resistance as well asbeing of use in forming the more conventional firm, highly viscous gels.

While the gelling systems of the prior art provide satisfactoryperformance for most aqueous compositions based on inorganic oxidizingsalts which are to be of relatively high viscosity, renewed interest inexplosives based on nitric acid, i.e., compositions sometimes referredto as Sprengel explosives, has presented new problems since the knownthickening and gelling systems are not satisfactory in the strong acid.For example, explosives based on concentrated nitric acid as the primaryoxidizing component exhibit exceptionally high acidity and oxidizingcapacity which are particularly hazardous in fluid compositions.Further, the use of these compositions in wet conditions is accompaniedby generation of high temperatures due to dilution of nitric acid withwater. Gelling systems of the types used in compositions based oninorganic oxidizing salts tend to decompose under acidic conditions. Inaddition, these gelling systems in general require careful control of pHduring formation, which control is not possible in the nitric acid basedcompositions, and are not operable in a highly acidic medium. Thickeningof the nitric acid based compositions, e.g., by inorganic fillers orlinear polymers, does not provide stable, cohesive, waterresistantresistant compositions having premium explosive properties.

SUMMARY OF THE INVENTION Accordingly, there is still a need for aqueousacidic compositions having a gelling system which can be used in a widerange of acidic compositions to give stable, water-resistant cohesiveproducts ranging from pourable, yet water-resistant fluids to rigidgels. The instant invention provides compositions of improvedhomogeneity, water resistance and stability which help meet this need.

The instant invention provides an improvement in gelled aqueous acidiccompositions, the improvement comprising a gelling system comprising thein situ cross-linked reaction product of at least one polymer containinga plurality of pendent groups selected from amide and nitrile functions,the amide nitrogen atoms hearing at least one hydrogen, and at least onemonomer containing a plurality of -CH OR groups bonded to amidonitrogen, wherein R is selected from hydrogen and lower alkyl of up tofour carbon atoms. Preferably the polymer comprises about from 0.1 to 10percent by weight of the acidic composition and the monomer comprisesabout from 0.5 to 50 percent by weight of the polymer. While the instantinvention is useful for gelling various acidic compositions such asnitric acid, to facilitate their handling and use, it finds particularutility when used in conjunction with acidic explosive compositionscomprising one or more fuels and an oxidizing component, This inventionfurther provides a process for the manufacture of these gelledcompositions which comprises bringing into contact, in an aqueouscomposition having a pH of less than about 6.0, at least one polymercontaining a plurality of pendent substituent groups selected from amideand nitrile functions, the amide nitrogen atoms bearing at least onehydrogen, and at least one monomer containing a plurality of -CH ORgroups bonded to amido nitrogen, wherein R is as defined above.

DESCRIPTION OF PREFERRED EMBODIMENTS The gelling system of thisinvention can be used with a wide range of acids including the commonmineral acids such as nitric acid, perchloric acid, sulfuric acid,hydrochloric acid, and phosphoric acid and water soluble or miscibleorganic carboxylic acids having a dissociation constant in water of atleast about 1X10 such as lower aliphatic monocarboxylic acids. These caninclude, for example, formic, acetic, propionic, butyric or isobutyricacid, lower aliphatic diand polycarboxylic acids of two to seven carbonatoms such as oxalic acid, malonic acid, succinic acid, and glutaricacid. The pH of the acidic compositions is less than about 6.0 andpreferably less than about 5.5. Of the above-named acids, the mineralacids and salts derived therefrom whose aqueous solutions are acidic,e.g., ammonium nitrate, are particularly well suited for forming thegelled structures of this invention. in gelling organic acids, thepresence of small quantities of a mineral acid can be desirable to speedgelation. Aqueous nitric acid and aqueous solutions of ammonium nitrateare particularly preferred acidic compositions to be gelled inaccordance with this invention since, as will be described andexemplified more fully hereinafter, there is a particular utility forthese inter alia in the formulation of explosive compositions. Nitricacid of about from 5 to 99 percent strength can be used; but nitricacids having concentrations of greater than 50 percent are most oftenused, and concentrations of about from to 98 percent are particularlypreferred.

In addition to its usefulness in gelling substances which are consideredas acids per se, the gelling system of this invention also finds utilitywith aqueous acidic solutions of compatible substances. Examples of suchsubstances include: ammonium nitrate, ammonium perchlorate, ammoniumchlorate, am-

wherein X is selected from CN and and the Rs can be the same ordifferent and each is independently selected from the group consistingof hydrogen, lower alkyl, hydroxyalkyl, or cyanoalkyl radicals having upto four carbon atoms, and

2. a polymer containing recurring units of the formula OOH wherein R isas defined above.

Examples of such polymers which are especially suitable for use inaccordance with this invention from the viewpoint of solubility anddispersibility in the liquid phase of the acidic compositions andavailability at reasonable cost include poly(acrylic amides) which arepolymers of acrylamide or methacrylamide, polymers of N-substitutedderivatives of acrylic amides such as N-methylacrylamide,N-ethylacrylamide, and N-methylmethacrylamide, and polymers ofhydroxyalkyl derivatives of amides such as d,2-hydroxyethyl acrylamideand a-hydroxymethacrylamide. Examples of poly(acrylic nitriles) whichcan be used in this invention include polymers of acrylonitrile,methacrylonitrilc, a-butylacrylonitrile, and a-hydroxymethacrylonitrile.ln general, homopolymers of the above-mentioned acrylic amides ornitriles or their mutual copolymers are preferred polymers because oftheir low cost and ease of dissolution in percent, wide range of acidicliquids. Particularly preferred polymers are homopolymers of acrylamideand of acrylonitrile and copolymers of acrylamide and acrylonitrile inratios varying about from 1/20 to /l. Copolymers comprising at leastabout 2 percent of amide or nitrile units as defined above and thebalance other copolymerized units can also be used. Representativecopolymerizable monomers include acrylic monomers, e.g., acids such asacrylic acid, methacrylic acid, a-ethyl acrylic acid and a-propylacrylic acid; esters such as methyl acrylate, methyl methacrylate, ethylacrylate, n-butyl methacrylate and n-hexyl acrylate; cycloalkylsubstituted acrylics, e.g., cyclohexyl methacrylate; salts such assodium or ammonium acrylate or alkyl ammonium acrylates; hydroxyalkylacrylates, e.g., 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate;cyanoalkyl acrylics such as acyanoethylacrylonitrile; nonacrylicmonomers such as sodium styrene sulfonate, vinyl acetate, vinyl pyridineand vinyl pyrrolidone and mixtures of two or more of such monomers,providing the copolymer formed meets the solubility and stabilityrequirements set forth. Although low concentrations of monomers havingpendent amide or nitrile functions in the copolymers can sometimes beused, e.g., as low as l to 2 percent, these monomers usually willcomprise at least about 2 percent of the copolymer. Preferred polymersinclude vinyl addition polymers soluble in the systems used herein,preferably having a molecular weight of about from 50,000 to 6,000,000.Cross-linking monomers which can be used in accordance with thisinvention can be selected from any compound having a plurality of (CHOR) groups bonded to amido nitrogen. Each CH OR group can be bonded to aseparate nitrogen atom, forming a plurality of NCH OR groups, or,alternatively, two CH OR groups can be attached to a single nitrogenatom. Such monomers include, for example, poly(hydroxymethyl)ureas suchas N,N-bis(hydroxymethyl)urea, i.e., dimethylolurea;N,N'-bis(alkoxymethyl)ureas such as N,N-bis(methoxymethyl)urea and N,N-bis(cthoxymethyl)urea; poly(hydroxymethyl)aliphatic amides such asmethylene-bis-(N-hydroxymethylformamide), N,N-bis(hydroxymethyl)adipamide, N,N-bis(hydroxymethyl)sebacamide,N,NN-tris(hydroxymethyl)melamine, hexakis(hydroxymethyl)melamine,bis(hydroxymethyl)formamide, N,N-bis(hydroxymethyl)acrylamide;N,N'-(alkoxymethyl)aliphatic diamides such asN,N-bis(methoxymethyl)sebacamide; N,N-substituted dinitramines such asN,N'-bis(hydroxymethyl)hexamethylene dinitramine; N,N-

O substituted sulfamides such as N,N-bis(hydroxymethyl)N,N'-

dimethyl sulfamide and N,N'-bis(methoxymethyl)N.N'- dimethyl sulfamide;and N,N-substituted disulfonamides such as N,N-bis(hydroxymethyl)-l,6-bis(methylsulfonamido)hexane, and mixtures of two or more of theabove.

Of the above illustrative cross-linking monomers, N,N'-bis-(hydroxymethyl)urea is especially preferred for the compositions of theinstant invention.

The term soluble in the aqueous acidic component and similar terms asused herein, refers to components having appreciable solubility atambient temperatures, i.e., about 20 to 25 C., in the particularaqueous, acidic component to be gelled. In general, this solubilityshould be at least about 10 percent by weight and preferably appreciablygreater, e.g., 50 percent or more. The reaction between acrylic polymerand cross-linking monomer should not preferentially form products whichseparate, e.g., by precipitation, from the aqueous acidic composition oragglomerate into flocculates or lumps." Cross-linking of the polymerchains forms a structure which is a gel rather than a precipitate. Thisgelled structure swells in and holds the aqueous, acidic composition andis of substantially constant composition throughout. The gelledcross-linked structure contains a relatively low ratio of polymer solidsto liquid phase, e.g., less than about 1 to 10, this ratio being roughlyequal to the weight ratio of combined polymer and monomer to the liquidphase, in contrast to precipitates or agglomerates in which there is ahigh ratio of polymer solids to liquid phase.

The gelled compositions of this invention are stable. That is, there islittle or no degradation of the polymer, cross-linking monomer or theirreaction products in the aqueous acidic composition to be gelled. Sinceprolonged stability is particularly desirable, stability refersparticularly to absence of degradation of a cross-linked system whensubjected to accelerated thermal stability tests which involve heatingthe sample at a temperature of 50 C. (l22 F.) for a period of at least 8to 12 hours.

Strength, when used herein with regard to acids, particularly to nitricacid, expresses in percent the relationship between the weight of l00percent (dry) acid and the weight of acid plus water in the particularacid.

The polymer for the gelling system preferably is provided as preformedpolymer. However, if desired, the polymer can be formed in situ in theacidic liquid in the presence of free-radical polymerization initiatorswhich are soluble to the extent of at least about 0.] percent in theacidic liquid. Suitable initiators include sodium, potassium andammonium salts of inorganic peracids; hydrogen peroxide; and organicperoxide and azo catalysts. Generally, persulfates are preferred. Thepersulfate ions, which are introduced as a soluble persulfate salt, canbe used along in the solution of inorganic oxidizing salt to promote thepolymerization reaction or an added reducing agent can also be employedto form a redox couple.

Formation of firm gel compositions can be completed in reasonably shorttimes, e.g., less than about 30 minutes, at temperatures of about 20 to25 C., particularly in strong oxidizing acids such as nitric acid. Rapidgelling is facilitated by using polymers of relatively high molecularweight, i.e., of one up to 6,000,000 or higher for polyacrylamide.

Preformed polyacrylamides which can be used in this invention includeCyanomer" P250, commercially available from American Cyanamide andPolyhall 295M commercially available from Stein Hall. Particularlypreferred polyacrylonitriles are Orlons, commercially available from DuPont and those prepared by emulsion polymerization Wham techniquesaccording to Sorenson and Campbell, Preparative Methods of POlymerChemistry, p. 169. Preferred copolymers consist of 2 to 25 percentacrylamide and 98 to 75 percent acrylonitrile prepared by emulsionpolymerization in accordance with Encyclopedia of Polymer Science andTechnology, Vol. I, p. 400; these copolymers have intrinsic viscositiesin 0.1 percent solutions in dimethylformamide at 30 C. of 8.0 to 10.0.As will be exemplified below, gels of very desirable properties can beformed from lower molecular weight polymers but higher molecular weightpolymers form gels more rapidly at lower temperatures and, in addition,usually require the use of less cross-linking monomer to provide gels ofequivalent properties, other ingredients and conditions remaining thesame.

The amide monomers employed for in situ polymerization in the explosivecompositions of this invention need not be highly purified. For example,crude acrylamide sulfate obtained by the hydrolysis of the correspondingnitrile, acrylonitrile, in the presence of concentrated mineral acid,e.g., sulfuric acid, can be used directly without purification. Thepresence of the minor residual amounts of mineral acid in the crudemonomer catalyzes the cross-linking reaction making possible faster geltimes and exerts no detrimental effect in the explosive composition.Additional acid, such as sulfuric acid, can be added in amounts of aboutfrom 0.5 to 5 percent as a positive catalyst to hasten gelling of theaqueous phase of the compositions.

The amount of polymer used in the gelling system will generally varyfrom about 0.1 to percent by weight of the liquid acidic composition andpreferably about from 0.5 to 5 percent by weight. About from 0.5 to 50percent of the crosslinking monomer based on the weight of the acrylicpolymer will usually be employed.

Preparation of the gelled compositions of this invention can beaccomplished by simply incorporating the polymer (preformed or formed insitu) and cross-linking monomer into the liquid acidic medium. There isno need for any catalyst and reaction between the polymer andcross-linking monomer in most cases begins shortly (within seconds)after addition of the polymer and monomer. Usually the polymer isadmixed with the acidic composition and the cross-linking monomersubsequently added to the composition.

ln general, gels form more rapidly when heat, e.g., of about from 30 to80 C., is applied than when the reaction is carried out at or nearambient room temperature. However, when the acidic composition is also astrong oxidizer and particularly when it is nitric acid, heating totemperatures above about 50 C. preferably should be avoided. In thepreparation of blasting compositions based on aqueous solutions ofinorganic nitrate it is particularly convenient to use concentratedaqueous solutions of ammonium nitrate commonly known in the art asammonium nitrate liquor, the aqueous liquid phase of the compositionbeing provided for the most part by this solution. In forming the gelledcompositions of this invention care should be taken that allingredients, viz, the polymer, cross-linking monomer and, if desired,any solid to be dispersed in the gel, are uniformly dispersed throughthe composition. Agitation used for blending and dispersing ofcomponents is desirably continued until the composition is gelled,particularly when particulate solids for example, fuels or sensitizerssuch as TNT, smokeless powder and/or aluminum used in explosivecompositions, are to be distributed uniformly through the gel matrix. Insome instances, for example, in explosive compositions which are tocontain a high percentage of solid TNT or when a solid which inhibitspolymerization or the cross-linking reaction is to be incorporated inthe compositions, all ingredients except such additives can be mixed andgelled and such additives blended into the gel formed.

When the polymer is to be formed in situ, the rate of polymerizationand, in some instances, product consistency can be adversely affected bythe presence of nitrogen oxides and oxygen, either in dissolved form oras the gases, and by the presence of large amounts of compoundsconventionally used to inhibit free-radical polymerization of themonomers. Compensations for these variations can be provided, whennecessary, by increasing the concentrations of polymerization promoters.An alternative and generally more economical expedient, however, is toreduce the concentrations of these polymerization-retarding componentsprior to the polymerization. In the case of nitrogen oxides and oxygen,this can be accomplished by carrying the polymerization out under ablanket of an inert gas, typically nitrogen. To further eliminatepolymerization inhibiting concentrations of nitrogen oxides and/oroxygen, the components of the blasting composition, particularly theaqueous solution of inorganic oxidizing salt, can be sparged with theinert gas. When preformed polymer is used, as is preferred, there is noneed to sparge the components.

The rate of gelling and the viscosity of the gelled composi tions ofthis invention can be varied according to the needs of a particularapplication. In general, the rate of gelling and the viscosity of thegel can be increased by increasing the percentage of polymer in thesystem, by increasing the relative proportion of cross-linking monomerused for a given quantity of the polymer, by increasing the molecularweight of the polymer employed in the system, or any combination of theabove.

The gelled compositions based on an inorganic oxidizer can be employedfor a variety of applications in which liquid aqueous acidiccompositions are ordinarily employed, as an acidifying agent inmineralogical and other processes, in preparing salts, and in likeoperations. The gelled nitric acid compositions find particular merit asan oxidizing or nitrating acid in chemical synthesis in suchapplications when delayed action is desirable or required; inasmuch asthe gels tend to release the acid slowly.

Several of the gelled acidic compositions based on nitric acid or anoxidizing salt are inherently satisfactory as detonating explosiveswithout further additives, i.e., they can be detonated withmoderate-strength primers in diameters of 6 inches or less undermoderate conditions of confinement, such as provided by a borehole or acontainer of moderate wall thickness. However, for explosiveapplications, the compositions of this invention also preferably containone or more fuels and/or sensitizers which are stable in the acid of thestrength used in preparing the gels. Examples of nonexplosive fuels arethe monoand dinitro aromatic hydrocarbons, such as nitrobenzene,o-mononitrotoluene and dinitrotoluene; liquid and solid hydrocarbons andhydrocarbon fractions, particularly refined petroleum and mineral oilsand the aromatic hydrocarbons, such as benzene, toluene, and thexylenes; carbohydrates, including various cellulose and starch products,e.g., cornstarch, potato starch, wood and paper pulps and sugars;siliceous fuels, including silicon itself and mixtures and alloys ofsilicon with heavy metals, e.g., ferrosilicon; and sulfurous fuels suchas sulfur itself and pyrites. Metal fuels such as aluminum orferrophosphorus are also useful in some of the gelled compositions,provided that they are, or can be made, sufficiently resistant to attackby the nitric acid. The gel copolymer per se acts as a fuel and exceptas otherwise indicated is included in calculating the amount ofnonexplosive fuel and oxygen balance. Ordinarily, the gels for use asexplosive compositions will be formulated to have an oxygen balance ofabout from -25 to +10 percent.

in addition to the nonexplosive fuels and/or sensitizers named above theexplosive compositions of this invention can, in some embodiments,contain one or more additives of the art-recognized self-explosive type,provided that such additive is stable in the strengths of acidiccomposition used in preparing the gels. TNT, for example, exhibits ahigh degree of stability in all strengths of aqueous nitric acid andammonium nitrate liquors and hence is a particularly useful additive ofthe self-explosive type. Examples of other self-explosive componentswhich can be used in the compositions of this invention are RDX, HMX,tetryl, PETN, nitrocellulose, smokeless powder, and other organicnitramines, nitrates and nitrocompounds. For reasons of economy andcompatibility, TNT is the preferred self-explosive for use in thecompositions of this invention. The TNT or mixtures thereof e.g., withammonium or sodium nitrate) can be introduced into the compositions inthe form of crystals, grains, pellets, flakes, or other particulate formwhich allows ready dispersion thereof. In general, up to 85 percent, andpreferably up to 40 percent, by weight of self-explosive additive basedon weight of the composition can be used.

Stable, gelled nitric acid compositions found especially economical andefficient as detonating explosives comprise a uniform blend of:

a. about from 25 to 95 percent by weight of aqueous nitric acid having astrength of about from 50 to 99 percent, and preferably 65 to 98percent; b. about from to 30 percent of a nonexplosive fuel, preferablyselected from siliceous fuels, light metals, liquid and solidhydrocarbons, carbohydrates, sulfur, monoand dinitro aromatichydrocarbons, and mixtures of such fuels and/or sensitizers; c, up toabout 40 percent of a self-explosive sensitizer, particularly TNT; d. upto about 50 percent of an inorganic oxidizing salt, typically aninorganic nitrate; and e. an in situ copolymerization product of 1.about from 0.1 to percent and preferably 0.2 to 5 percent, based on theweight of aqueous nitric acid of at least one polymer as defined above,which preferably is formed from acrylamide, acrylonitrile,methacrylonitrile, or methacrylamide or is a copolymer ofmonoethylenically unsaturated monomers of this group, and

2. about from 0.5 to 50 percent and preferably 0.1 to 10 percent byweight based on component (1) of a crosslinking monomer as definedabove, and preferably N,N'-bis(hydroxymethyl)urea,

Particularly preferred explosive compositions based on inorganicoxidizing salts and having an oxygen balance of about from 25 to +10percent comprise:

a. about from to 70 percent ammonium nitrate;

b. up to 40 percent and preferably 10 to percent sodium nitrate;

c. up to 40 percent and preferably 10 to percent self-ex plosive;

d. up to 30 percent of metallic fuel, preferably 2 to 20 percent ofaluminum and/or 5 to 25 percent of ferrophosphorus; up to 10 percent ofnonexplosive fuel, preferably selected from carbonaceous, siliceous orsulfurous fuels or combinations thereof;

. from 5 to 45 percent and preferably 10 to 30 percent of water; g. anin situ formed product of 1. about from 0.1 to 10 percent and preferably0.2 to 5 percent based on the aqueous phase of the composition of atleast one polymer as defined above, and preferably a poly(acrylic amide)and 2. about from 0.5 to 50 percent based on the weight of the polymer(1) of a cross-linking monomer as defined above, which monomer ispreferably N,N'-bis(hydroxymethyl)urca.

In general, the gelled blasting compositions of this invention areprepared by blending of the ingredients, e.g., in a rotarytype mixersuch as a Lightnin AG-IOO mixer, keeping in mind the same generalconsiderations for the control of the process as were discussed above.As mentioned, it is generally preferred to use preformed polymer toavoid the need for sparging and for maintaining the components whilebeing blended under an inert gas atmosphere until polymerization iscomplete. Usually, the nitric acid is introduced into the mixing vesselfirst and the other ingredients added individually thereto while thecontents of the vessel are being agitated. The cross-linking monomer isusually the last ingredient added.

Agitation is usually continued until after the composition is gelled,particularly when the added fuels or sensitizers are solids such as forexample, ferrosilicon, sulfur, aluminum, silicon, or starch, which mustbe distributed uniformly throughout the gel matrix. Where fuels or otheradditives of marginal stability or additives which inhibitpolymerization are to be incorporated in the compositions, allingredients except such additives can be mixed and gelled as previouslydescribed, then such additives blended with the finished gel.

As indicated above, for explosive applications preferred ranges ofnitric acid strength are about from 60 percent (corresponding to amaximum water content of about 40 percent) to 97 percent. In general,the unit or bulk strength ofan explosive composition based on gellednitric acid increases with increasing strength of the nitric acidgelled. Accordingly gels of nitric acid of percent strength or higherare usually employed where high bulk strength is a requisite, e.g., inthe bottom of a borehole. The bulk or unit strength of an explosivecomposition, its relative ease of initiation, and its minimum criticaldiameter can also be regulated to a large degree by the type andquantity of fuel and/or sensitizer employed. Organic nitro compounds,typically mononitrotoluene, or dinitrotoluene, or in particular aself-explosive composition, especially TNT, are incorporated to providecompositions which are easily initiated, e.g., by a relatively smallprimer or by a blasting cap, in some cases, in small diameters. in manycases, a combination of fuels will be employed within the range ofproportions indicated to give a composition having the desired physicaland explosive properties.

Preferred gelling systems for explosive compositions comprise polymersof acrylonitrile, acrylamide, methacrylonitrile or methacrylamide, orcopolymers thereof. The cross-linking monomer preferred isN,N-bis-(hydroxyethyl)urea. In addition to being readily available atreasonable cost, these compositions are particularly effective inproviding firm cohesive gels having viscosities within the desired rangeof l00,000 to l0,000,000 c.p.s. high surface tension as evidence by lackof stickiness or tackiness, ready workability, flexibility, waterresistance, and other desirable physical characteristics in the asmadestate. Further compositions including these preferred gelling systemsretain their initial physical and explosive properties during storageafter production. The preferred gelling systems also allow relativelywide latitude in the consistency of the explosive product made to fitthe needs ofa particular type of blasting.

This invention therefore provides simple and effective modified aqueousacidic compositions which are easier and safer to handle than thoseknown heretofore and which have controlled free acidity and excellentstability. These and other properties of the gelled acidic compositionsof this invention make the products of this invention particularlysuitable as propellants, cleaning solutions, oil well treating agents,and etching compositions, in chemical syntheses, as an acidifying agentin mineralogical processes, in fertilizers, and in other uses whereaqueous acid is now employed. In addition, physical properties such ascohesiveness, controlled flexibility and consistency and the ability tomaintain dispersion of solids therein as well as their explosiveproperties make compositions of this invention, particularly thosecontaining conventional fuels and sensitizers, readily adaptable toformulation in fixed plant facilities as well as mobile and other onsiteequipment.

In the following examples which illustrate this invention, parts,percentages and ratios are by weight unless otherwise indicated. In thefollowing examples, the terms noted below mean the following:

Very Firm-Viscosity of about from 3,000,000 to 10,000,000 c.p.s. asmeasured with TR spindle at 0.5 r.p.m. on the Brookfield SynchrolectricViscometer.

FirmViscosity of about from 1,000,000 to 3,000,000 c.p.s. measured witha TE spindle at 1.0 r.p.m. on a Brookfield Synchro-lectric viscometer,Model RVT, with helipath attachment.

Medium Firm-Viscosity of about from 400,000 to complete. The reactiontemperature is as noted in the table.

1,000,000 c.p.s. using the same conditions of measure- Gelation timerefers to the interval of time between the addiment on the viscometer.tion of the last ingredient and the first appearance of gelledWeak-Viscosities generally less than about 400,000 c.p.s., product. Noneof the gel products show visible signs of deterigenerally 200,000 to400,000 c.p.s. oration at ambient temperatures (ca. 20 to 25 C.) over 1.Changes in spindle and r.p.m. necessary to obtain accurate periods of 1week, the maximum periods of observation. readings. Explosivecompositions are provided from the compositions in examples l-34 byincorporating in the gelled composition a EXAMPLES fuel, particularly acarbonaceous fuel or a monoor dinitro- Gelleci nitric acid compositionsof this invention are substituted aromatic compound, to give an oxygenbalance of Aq. HNOa,

strength Polymer percent Temp., Gel product description Example percentof HNOs Grosslinking monomer, percent of polymer Additive C. and geltime 70 Polyacrylamide, 1.2 N,N-bis(hydroxymethyDurea, 6.6 55 Medium gelin 45 sec. 70 do 1 N,N-bis(hydroxymethyl)urea, 1.6 55 Medium firm gel in2 11111]. 70 do 1 N,N-bis(hydroxymethy1)urea, 3.3 25 Firm gel in 45 min.70 Polyacrylamide, 3 N,N'-bis(hydroxymethyl)urea, 13.. 25 Firm gel n 48min. 70 Polyacrylarnide, 2 bis(hydroxymethyl)nrea, 55 Firm gel n 140sec. 80 Polyacrylaimde, 2 Bis(hydroxyn1ethyl)urea, 4 50 Firm gel in 27sec. 70 Polyacrylamlde, 0.75... N,N-bis(hydroxymethyl)urea, 2.75 50 Weakgel in 9 mm.; firm to medium gel in 2 hrs.

8. 70 Polyacrylamide, 1.2- N,N-bis(l1ydroxymethyDurea, 6.6 25 Weak gelin 25 milk;

firm gel overnight.

9 80 do 1 N,N-bis(hydroxymethyDurea, 3.3 35 Medium gel overmght(thickened ca. 1 hr.).

10 6O do do 35 Weak gel in 12 mln.;

medium gel in 14 min.

11 70 .do do NH NO 35 Medium gel in 15 mm.

percent 12. 70 do N,N-bis(hydroxymethyl)adipamide, 20 55 Gieltin 47 se(expl ined a er 1 70 Po1yacrylamide, 1.6N,N-bis(hydroxymetbyl)adipamide, 10 55 Medium firm gel in 104 sec.

14 70 Polyacrylamide, 2 N,N,N-tris(hydroxymethyDmelamine, 10 50 H g lflyi l' yellow ge m min.

70 Polyacrylaruide, 1.6 N,N,N-tris(hydroxymethyDmelamlne, 5.0 Weak gelin 1 hr- 70 .do 1 Bexakis(hydroxymethy1)melamine, 12.5 50 Firm gel in1mm;

highly expanded by 70 Polyacrylamide, 1.2N,N-bis(hydroxymethyl)sebacamide, 13.3 50 weal; g l 8 70 do 1N,N-bis(methoxymethyl)urea, 3.3 50 Medium g In 90 95 Polyacrylamide, 0.6N,N-bis(hydroxymethyl)urea, 8.3 25 Weak gel in 3 his;

medium gel in I? days.

2 75 Polyacrylonitrile, 1 N ,N-bis(hydroxymethyDurea, 5 50 Medium fi 81n 3 21 15 do i N,N-bis(hydroxymethyl)urea, 10 5 Medi fi gel In 6 mm;became firmer on standing.

95 Polyacrylonitrile, 0.75 N,N-bis(l1ydroxymethy1)urea, 13.3 25 M di mfi m gel In 26 min.

23 80 Polyacrylonitrile, 4 N,N-bis(hydroxymethyl)urea, l0 5 Ch e g 111 lmin.

24 80 Polyacrylonitrile, 4 N,N-bis(hydroxymethyl)urea, 10 50 ed fi g 11113 25 70 Copolymer of acryl- Bis(hydroxymethyl)urea, 1.6 Medium firm gelin 3 onitrile and acrylmin.; firm gel in 5 amide, 1.2. i

26... 70 Copolymer of acryl- Bis(hydroxymethyl)urea, 5.3 25 Weak gel in12 min.

onitrile and acrylamide, 0.75.

75 Copolymer of acrylamide N,N-bls(hydroxymethy1)urea, 6.6 25 Mediumfirm gel in 20 and acrylonitrile, 1.2. hrs. 75 Copolymer of acrylamidedo H 35 Medium firm gel in and acrylonitrile, 1.2. min. 70Polyaerylamide, 1.2 N,N-bis(hydroxymetbyl)hexamethylene' 35 Weak gel in2 hrs.

dinitramlne, 10. 70 do 1 do Weak gel in 7.5 min. do 1N,N-bis(hydroxymethyl)-1,6-bis(methyl- 45 Medium gel in 5 min.

sulfonamide)hexane, 6.6. 70 do 1 N ,N-bis(hydroxymethyl)-1,6-bis(methyl-45 Weak gel in 5 min.

sulfonamido)hexane 3.3. 70 do 1 N,N-bls(hydroxymethyl)forrnamide ,6.6 25Medium firm gel in 1% hrs., firm overnight. 34.. 70 d0 .do 50 Firm gelwithin 25 min.

1 Cyanomer P250polyacrylamide available commercially from AmericanCyanamid 00.; molecular weight, 5-6 million.

2 Acrylamide polymerized in situ in the nitric acid at 15 C. usinginitiator system of 0.14% ammonium persulfate, 0.04% (31150451120 and0.008% N2H4.H2O; molecular weight, ca. to 1 million.

3 Cyanomer P26low molecular weight copolymer of acrylamide and acrylicacid available from American Cyanamid Co.

4 Polyhall 295-M-polyacrylamide, commercially available from Stein-HallCorp., contains about 12% acrylic acid in the form of sodium salt;molecular weight, 5-6 million.

5 High molecular weight polyacrylonitrile prepared by emulsionpolymerization as by Sorenson and Campbell, Preparative Methods ofPolymer Chemistry, p. 169; molecular weight, 1.5 million; i n 17.0 inDMF at 25.

6 Low molecular weight polyacrylonitrile prepared by recipe in Sorensonand Campbell, p. 168; 'Iin =2 in DMF at 25.

7 Scrap Orlon" polyacrylonitrile fiber; molecular weight, 50,000-70,000.

B High molecular weight copolymer prepared by emulsion polymerizationand comprising 25% acrylamide and acrylonitrile; prepared by emulsionpolymerization by recipe in Encyclope a of Polymer Science andTechnology, vol. I, p. 400.

Low molecular weight copolymer prepared by emulsion polymerizationcomprising 20% acrylamide and acrylonitrile; prepared by methoddescribed in reference cited for footnote 8.

Copolymer comprising 12.5% acrylamide and 87.5% acrylonitrile, prepar edby method as described in reference cited for footnotes 8 and 9. above.

prepared from the materials noted in table 1. The polymer is about froml0 to 0 percent. first dissolved and admixed in nitric acid of thestrength indicated and the cross-linking monomer is then added withagitation, which is continued until gelation is substantially 75 Aqueoussolutions of ammonium nitrate (pH of about 5.5)

EXAMPLES 35-43 polyacrylamide (commercially available as Cyanomer P-250)with N,N'-bis(hydroxymethy)urea. Various fuels and sensitizers as shownare incorporated in the formulations by first thoroughly blending allcompositions except the N,N- bis(hydroxymethyl)urea in the aqueousnitric acid, then adding this ingredient and finally continuing mixingfor about l0 to minutes, during which time the reaction runssubstantially to completion.

The gelled formulations are loaded into S-inch-diameter TABLE 2 Polymer,percent of aq.

Example N H4NO3 Crosslinking monomer, percent of polymer NH4 Additives,percent of aq. Temp., Gel product description and gel timePolyacrylamide 1 2 N,N-bis(hydroxymethyl)urea, 6.6 60 Medium firm gel in15 sec. N,N-bis(hydroxymethyl) urea, 3.3 60 Weakgel in 90 sec.N,N-bis(hydroxymethyl)urea, 6.6

30 Medium firm gel in 2% min.

38 am N,N-bis(hydroxymethyl)urea, 2.7 NaNO3, 60 Firm gel in 13 sec.

39.. Polyecrylamide, 0.64 N,N-bis(hydroxymethyburea, 3.1 NaNOz, 17 45Medium firm gel in 5 sec. 40 olyacrylamide, 2.0N,N-bis(hydroxymethylgure 1-. 45 Firm gel in 3 min.

41 o. N,Nbis(hydroxymethyl 45 Medium firm gel in 3 min. 42 do.-. N, S( yy l 60 Firm gel in l min.

43 do N ,N-bis(methoxymethyl)urea, 6.6.. 25 Firm gel in 6 min.

Explosive compositions are formulated from the aqueous gels of theforegoing examples by the admixture of at least one fuel or sensitizerin the proportions indicated above. For example, if about from 10 topercent TNT is admixed with the finished gels, a cap-sensitive explosivecomposition results having an oxygen balance of about l0 to 0 percent.NCN gels are provided when the fuel used is a nonexplosive andparticularly when a blend of carbonaceous, sulfurous, and, if desired,metallic fuels are employed to give compositions having an oxygenbalance of about from l0 to 0 percent.

EXAMPLES 44-45 Gelled explosive compositions based on ammonium nitrateand of the formulation shown below are prepared as follows using agelling system wherein polyacrylamide is formed in -situ andsubsequently cross-linked.

To aqueous ammonium nitrate solution at 65 C. are added sodium nitrateand monomeric acrylamide. Mixing is begun and continued about 3 minutesto assure uniform dispersion of ingredients. A 50 percent aqueoussolution of ammonium persulfate is then added to initiate polymerizationof acrylamide in situ.*( *The combining of ingredients and particularlythe in situ formation of polymer are conducted under a blanket ofnitrogen.) After about 10 minutes pellets of TNT are blended into thecomposition until complete incorporation and dispersion thereof areobserved. N,N.-bis( hydroxymethyl)urea is then added as a cross-linkingagent for the polyacrylamide. Gel formation is observed in about 5minutes after this addition. The firm, gelled compositions aretransferred into 5-inch diameter polyethylene bags (25 lb./bag). Whendetonation of the composition is initiated, in air, by two conventionalprimers, each comprising 1 .lb. (454 g.) of cast TNT, the compositionsdetonate completely at the velocities shown.

Catalyst to assure acidity.

EXAMPLES 46-47 Firm, gelled explosive formulations based on nitric acidas the oxidizing agent are prepared of the formulations shown below.Each composition is gelled by the in situ reaction of cartridges (20lb./cartridge) and tested unconfined at 32 F. in each case, detonationof the charge is effected by a primer comprising 1 lb. (454 g.) of castTNT.

An explosive formulation of the composition summarized below is preparedbasically as described in examples 46-47. This composition, which formsa firm gel, is transferred into 2V4-inch-diameter containers (200g./container) and tested by actuating by a 50 g. RDX pellet.

75% HNO 85.1 Starch 2.5 Mineral Oil 1 1.1 Copolymcr of 75/25 acrylo- 1.2nitrile/acrylamide Detonation Velocity, m./sec. ca. 5,000

EXAMPLES 49-5 3 Explosive compositions as shown in table 3 are preparedas described in examples 46-47 using an aromatic nitro compound as asoluble sensitizer-fuel and copolymers of acrylamide and acrylonitrileas the polymer. D indicates the composition detonates when actuated by aconventional primer comprising 1 lb. of TNT.

TABLE 3 Example 75% ENG; 78.0 78.0 78.0 72.0 78.0

Copolymer:

Acrylic terpolymer 25/75 acrylamidelacrylonitrile 1.2

10/90 acrylamidelacrylonitrile 1.2

5/95 acrylamide/acrylonitrlle-.. 1. Nitrobenzene 20 8 20.8 20.8

Dinitrotoluene, 26

N ,N'-bis(hydroxymethy1)urea 0. 05 0. 05

Gelling temperature, 70 70 70 70 70 Gel time, hr 1% 2% 1% 1% 4Detonation results D D D D D Terpolymer consistin essentially of 93.7%polyacrylonitrile, 6% ZP J!9E 1? s e ljp mt t fie wee EXAMPLES 5456 r ORH 1 CHz-HCH H Acids indicated in table 4 are gelled by the reaction of005 l polyacrylamide (Cyanomer P-250) and N,N'-bis(hydrox- 5ymethyl)urea in situ basically as described inexamples l-34. 1]) R TABLE4 N,N'-bis(hydroxymethyD- I Polyacrylurea, ercent Temp., Example Acidamide, of po yacryl- C. Additives Results percent amide 64 37% H01 2.035 Finn gel instantly. 56 37% H01 2.0 10 25 o. 56 60% acetic acid 2.0 1045 H2804, 1.6%. Thlcknenlng in 10 min.;

firm gel overnight.

EXAMPLE 57 wherein R is as defined above.

A copolymer of methyl vinyl ether and maleic= anhydride (commerciallyavailable as Gantrez AN) is reacted with aqueous ammonia to give apolymer ofthe structure OCHg This polymer is dissolved in 80 percentnitric acid, the amount of polymer being 8 percent by weight of theacid. To this solution at 50 C. is then added 2.5 percent (based on theweight of the polymer) of N,N'-bis(hydroxymethyl)urea. A weak gel formsin IQ minutes.

I claim:

1. ln gelled aqueous acidic compositions, the improvement whichcomprises providing a gelling system comprising the in situ cross-linkedreaction product of A. at least one polymer containing a plurality ofpendent groups selected from amide and nitrile functions, the

amide nitrogen atoms hearing at least one hydrogen, and

B. at least one cross-linking monomer containing a plurality of CH ORgroups bonded to amido nitrogen, wherein R is selected from hydrogen anda lower alkyl of up to four carbon atoms.

2. A composition of claim 1 wherein said polymer comprises about from0.1 to 10 percent by weight of the liquid acidic composition and themonomer comprises about from 0.5 to 50 percent by weight ofthe polymer.

3. A composition of claim 1 wherein the polymer is selected from thegroup consisting of:

A. polymers in which at least about 2 percent of the repeating units arewherein X is selected from CN and the Rs being independently selectedfrom the group consisting of hydrogen, lower alkyl, hydroxyalkyl orcyanoalkyl radicals having up to four carbon atoms, and

B. polymers containing recurring units of the formula 4. A compositionof claim 3 wherein the polymer comprises polyacrylamide. v

5. A composition of claim 3 wherein the polymer comprisespolyacrylonitrile.

6. A composition of claim 3 wherein the copolymer comprises a copolymerof acrylamide and acrylonitrile and each of said acrylamide andacrylonitrile comprises at least about 2 amethylenedinitramine.

12. A composition of claim 3 wherein the cross-linking monomer comprisesN,N-bis( hydroxymethyl l ,6- bis(methylsulfonamido)hexane.

13. A composition of claim 3 wherein the cross-linking rnonomercomprises bis(hydroitymethyDformamide.

14. A process for gelling aqueous acidic compositions which comprisesbringing into contact, in an aqueous composition having a pH of lessthan 6,

A. at least one polymer containing a plurality of pendent substituentgroups selected from amide and nitrile functions, amide nitrogen atomshearing at least one hydrogen and B. at least one cross-linking monomercontaining a plurality of CH 0R groups bonded to nitrogen wherein R isselected from hydrogen and lower alkyl of up to four carbon atoms.

15. A process of claim 14 wherein the polymer comprisesabout from 0.1 to10 percent by weight of the total composition and said monomer comprisesabout from 0.5 to 50 percent by weight of said polymer.

16. A process of claim 15 wherein the polymer comprises polyacrylamide.

17. A process of claim 15 wherein the polymer comprisespolyacrylonitrile.

18 A polymer of claim 15 wherein the monomer comprisesN,N'-bis(hydroxymethyl)urea.

2. A composition of claim 1 wherein said polymer comprises about from0.1 to 10 percent by weight of the liquid acidic composition and themonomer comprises about from 0.5 to 50 percent by weight of the polymer.3. A composition of claim 1 wherein the polymer is selected from thegroup consisting of: A. polymers in which at least about 2 percent ofthe repeating units are , wherein X is selected from -CN and , the R''sbeing independently selected from the group consisting of hydrogen,lower alkyl, hydroxyalkyl or cyanoalkyl radicals having up to fourcarbon atoms, and B. polymers containing recurring units of the formulawherein R is as defined above.
 4. A composition of claim 3 wherein thepolymer comprises polyacrylamide.
 5. A composition of claim 3 whereinthe polymer comprises polyacrylonitrile.
 6. A composition of claim 3wherein the copolymer comprises a copolymer of acrylaMide andacrylonitrile and each of said acrylamide and acrylonitrile comprises atleast about 2 percent of said copolymer.
 7. A composition of claim 3wherein the cross-linking monomer comprisesN,N''-bis(hydroxymethyl)urea.
 8. A composition of claim 3 wherein thecross-linking monomer comprises N,N''-bis(hydroxymethyl)adipamide.
 9. Acomposition of claim 3 wherein the cross-linking monomer comprisesN,N'',N''''-tris(hydroxymethyl)melamine.
 10. A composition of claim 3wherein the cross-linking monomer compriseshexakis(hydroxymethyl)melamine.
 11. A composition of claim 3 wherein thecross-linking monomer comprisesN,N''-bis(hydroxymethyl)hexamethylenedinitramine.
 12. A composition ofclaim 3 wherein the cross-linking monomer comprisesN,N''-bis(hydroxymethyl)-1,6-bis(methylsulfonamido)hexane.
 13. Acomposition of claim 3 wherein the cross-linking monomer comprisesbis(hydroxymethyl)formamide.
 14. A process for gelling aqueous acidiccompositions which comprises bringing into contact, in an aqueouscomposition having a pH of less than 6, A. at least one polymercontaining a plurality of pendent substituent groups selected from amideand nitrile functions, amide nitrogen atoms bearing at least onehydrogen and B. at least one cross-linking monomer containing aplurality of -CH2OR groups bonded to nitrogen wherein R is selected fromhydrogen and lower alkyl of up to four carbon atoms.
 15. A process ofclaim 14 wherein the polymer comprises about from 0.1 to 10 percent byweight of the total composition and said monomer comprises about from0.5 to 50 percent by weight of said polymer.
 16. A process of claim 15wherein the polymer comprises polyacrylamide.
 17. A process of claim 15wherein the polymer comprises polyacrylonitrile. 18 A polymer of claim15 wherein the monomer comprises N,N''-bis(hydroxymethyl)urea.